Cystic fibrosis (CF) is a lethal autosomal recessive inherited disease caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), which functions as a cAMP- dependent Cl channel at the apical membrane of epithelial cells, including those lining the airways. A critical issue in CF disease is the inability of the most common CFTR mutation, deletion of the phenylalanine residue at position 508 (?F508CFTR), to achieve the native, folded state required for its export from the endoplasmic reticulum (ER) and traffic to the epithelial cell apical membrane. Instead, ?F508CFTR protein is exclusively retained in the ER and degraded by the ubiquitin-proteasome system. Our understanding of CFTR biogenesis in its early stages is incomplete. Recent studies show that Derlin and its associated proteins play a critical role in ubiquitin mediated CFTR degradation. Our preliminary data suggest that the Derlin complex effectively degrades wt and ?F508 CFTR and that specific components of Derlin complex preferentially regulate ?F508CFTR degradation. Our hypothesis is that the Derlin complex is a key regulator of the early steps in CFTR biogenesis. The goal for this proposal is to identify components of the Derlin complex that recognize and extract CFTR from the ER, and to identify the basis for their selective degradation of ?F508CFTR. We will test four specific aims: (1) to define the role of Derlin complex in CFTR degradation; (2) to examine the role of lysine-linkage of polyubiquitin chains in CFTR biogenesis; (3) to identify the processes mediating CFTR retrotranslocation from the ER to the cytosol; and (4) to evaluate the ubiquitin E3 ligases that evoke ubiquitin- mediated CFTR degradation. Successful completion of this proposal will advance our understanding of early checkpoints in ?F508 CFTR biogenesis and provide a roadmap for identifying novel potential therapeutic targets to restore ?F508 maturation and function.